Remove 'undo' section from sample pinotrc file

Original nano commit: 5076
http://svn.savannah.gnu.org/viewvc?view=rev&root=nano&revision=5076
Original nano commit message:
	* doc/nanorc.sample.in: Remove âundoâ section which is now obsolete.
Remove 'undo' from list of valid keywords in pinotrc syntax highlighting

Original nano commit: 5077
http://svn.savannah.gnu.org/viewvc?view=rev&root=nano&revision=5077
Original nano commit message:
	Removing 'undo' from the valid options, so it gets coloured brightred.